1. Field of the Invention
The present invention relates to an apparatus for recording and/or reproducing a magneto-optical disc and is directed more particularly to an optical recording and reproducing apparatus using an erasable and rewritable optical disc.
2. Description of the Prior Art
When information is recorded on a recording medium, it is often required, for efficiently using the recording medium, to record information signals uniformly all over the recording medium so as not to leave unrecorded portions thereon. Now, assume a case where an information signal is to be recorded subsequent to the previously recorded signals on a cassette tape used by an ordinary tape recorder or a digital tape recorder (DAT). If the cassette remains loaded in the tape recorder in the same condition as it was when the previous recording was completed, the next information signal may be recorded without changing the condition of the tape. If the cassette is taken out of the tape recorder after a previous recording has been finished, the cassette may be subsequently loaded into the tape recorder again to record the information signal on the cassette tape. In other words, if the tape remains unchanged after the latest recording has been completed, that is, if the tape has not been rewound or rapidly forwarded, loading the cassette again into the tape recorder causes the beginning of the unrecorded portion to oppose the magnetic head of the tape recorder, so that an information signal can be recorded subsequent to the latest recorded location at a location immediately after the latest recorded portion by the magnetic head of he tape recorder. If previously recorded information signals are no longer necessary, an information signal may be recorded starting from any desired location of the tape.
However, if the above-mentioned cassette tape is once rewound to reproduce a signal recorded in a different location, it is difficult to quickly search for the head of the unrecorded portion subsequent to the previously recorded portion, thereby slowing down access to the end of the previously recorded portion.
Apart from the tape-shaped magnetic recording medium, there is also a magneto-optical disc considered as a recording medium. The magneto-optical disc is generally classified into a disc for reproduction only and a disc for optical recording. The latter is further classified into a so-called Write Once optical disc on which an information signal once written permanently remains recorded and a rewritable (or an erasable) optical disc which permits an information signal once written thereon to be erased and a different information signal to be written again in the same location.
With the rewritable or erasable optical disc, even if an optical pickup is held at the end location of a recording operation after it has been terminated, it is difficult, in the next recording operation, to return the spot position of a light beam emitted from the optical pickup to the end of the previously recorded portion, due to conditions of an objective lens of the optical pickup after the termination of the recording operation. Moreover, if the optical disc is replaced with another one or if the disc is removed from the optical disc recording and/or reproducing apparatus, it is impossible to quickly access, with the optical pickup, the beginning of an unrecorded portion subsequent to the previously recorded portion of the optical disc loaded in the optical disc recording and/or reproducing apparatus.
With an optical disc which does not permit recorded information signals to be erased or rewritten such as the Write Once disc, it is possible to access the beginning of the unrecorded portion by checking whether information signals have been recorded or not, however, such an access operation takes a long period of time. Similarly to the Write Once disc, with the erasable disc, it is possible to access the beginning of the unrecorded portion by checking whether information signals have been recorded or not, however, an access time is too long in this case, too. The erasable disc has another problem on accessing that the beginning of a portion to be recorded is not always limited in the unrecorded portion. For example, in such a case that a recording may be effected from the beginning of a portion in which an unnecessary or unwanted information signal for an optical disc is recorded, from a portion subsequent to a portion in which an information signal has been previously rewritten, or from a desired location of its mid portion, it also takes a long time to access one of these locations on the optical disc by the optical pickup Thus, it is not so easy to record a new information signal subsequent to a previously recorded portion of the optical disc by the optical pickup.